Basis of Presentation and Summary of Significant Accounting Policies New Accounting Policy (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	$ (1,514.7)	$ (1,584.1)	$ (1,750.7)	$ (1,367.7)	$ (1,481.9)	$ (537.4)	$ (558.1)	$ (410.1)	$ (6,217.2)	$ (2,987.5)	$ (2,131.6)
Marketing, general and administrative expenses									(3,032.4)	(1,589.8)	(1,038.3)
Special items, net									(28.1)	2,522.4	(346.7)
Income tax benefit (expense)									(53.2)	1,055.2	61.5
Net income (loss) from continuing operations	588.1	287.2	328.3	209.1	1,439.8	207.7	179.7	168.6	1,412.7	1,995.8	391.3
Net income (loss) attributable to Molson Coors Brewing Company	$ 588.8	$ 287.0	$ 329.9	$ 208.5	$ 1,439.3	$ 207.7	$ 177.9	$ 168.1	$ 1,414.2	$ 1,993.0	$ 395.2
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.73	$ 1.33	$ 1.52	$ 0.97	$ 6.70	$ 0.97	$ 0.84	$ 0.83	$ 6.56	$ 9.41	$ 2.11
Basic net income per share (in dollars per share)	2.73	1.33	1.53	0.97	6.70	0.97	0.83	0.83	6.57	9.40	2.13
From continuing operations (in dollars per share)	2.72	1.33	1.52	0.97	6.65	0.96	0.83	0.82	6.52	9.35	2.10
Diluted net income per share (in dollars per share)	$ 2.72	$ 1.33	$ 1.52	$ 0.96	$ 6.65	$ 0.96	$ 0.82	$ 0.82	$ 6.53	$ 9.34	$ 2.12
Consolidated Statements of Comprehensive Income (Loss)
Pension and other postretirement benefit adjustments, net of tax									$ 145.7	$ 53.8	$ 19.3
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax									(3.6)	(22.8)	(16.1)
Other comprehensive income (loss), net of tax									714.3	129.4	(833.2)
Consolidated Balance Sheets
Retained earnings	$ 7,206.1				$ 6,145.3				7,206.1	6,145.3
Accumulated other comprehensive income (loss)	(860.0)				(1,571.8)				(860.0)	(1,571.8)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests									1,436.4	1,998.9	398.5
Income tax (benefit) expense									(53.2)	1,055.2	61.5
Pension (benefit) expense									(67.8)	(11.6)	(30.1)
As Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	(1,520.3)	$ (1,589.6)	$ (1,756.1)	$ (1,372.9)	(1,485.6)	$ (541.3)	$ (562.2)	$ (414.0)	(6,238.9)	(3,003.1)	(2,163.5)
Marketing, general and administrative expenses	(779.4)	(782.8)	(781.2)	(702.8)	(753.9)	(278.9)	(313.6)	(250.9)	(3,046.2)	(1,597.3)	(1,051.8)
Special items, net	(3.7)	(4.1)	(16.5)	(3.8)	2,444.9	4.9	(34.5)	108.6	(28.1)	2,523.9	(346.7)
Income tax benefit (expense)	(392.4)	145.3	123.0	64.6	993.2	19.6	21.2	16.7	59.5	(1,050.7)	(51.8)
Net income (loss) from continuing operations									1,383.5	1,978.7	355.6
Net income (loss) attributable to Molson Coors Brewing Company	$ 580.4	$ 280.0	$ 323.3	$ 201.3	$ 1,438.4	$ 202.5	$ 172.3	$ 162.7	$ 1,385.0	$ 1,975.9	$ 359.5
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.69	$ 1.30	$ 1.49	$ 0.94	$ 6.70	$ 0.94	$ 0.81	$ 0.80	$ 6.42	$ 9.33	$ 1.92
Basic net income per share (in dollars per share)	2.69	1.30	1.50	0.94	6.70	0.94	0.80	0.80	6.43	9.32	1.94
From continuing operations (in dollars per share)	2.68	1.29	1.49	0.93	6.65	0.94	0.81	0.80	6.39	9.27	1.91
Diluted net income per share (in dollars per share)	$ 2.68	$ 1.29	$ 1.49	$ 0.93	$ 6.65	$ 0.94	$ 0.80	$ 0.80	$ 6.40	$ 9.26	$ 1.93
Consolidated Statements of Comprehensive Income (Loss)
Pension and other postretirement benefit adjustments, net of tax	$ 161.2	$ 0.0	$ 0.0	$ 0.0	$ 62.3	$ 0.0	$ 0.0	$ 0.0	$ 161.2	$ 62.3	$ 33.6
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax	2.3	6.7	6.7	1.6	10.5	6.9	7.0	7.0	17.3	31.4	37.5
Other comprehensive income (loss), net of tax									743.5	146.5	(797.5)
Consolidated Balance Sheets
Retained earnings	7,150.6	6,658.7	6,467.0	6,232.0	6,119.0	4,768.9	4,654.5	4,570.4	7,150.6	6,119.0
Accumulated other comprehensive income (loss)	(804.5)	(1,038.6)	(1,222.3)	(1,470.2)	(1,545.5)	(1,633.3)	(1,573.9)	(1,437.9)	(804.5)	(1,545.5)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests	1,407.2	822.3	536.2	207.8	1,981.8	541.2	337.4	163.5	1,407.2	1,981.8	362.8
Income tax (benefit) expense	(59.5)	332.9	187.6	64.6	1,050.7	57.5	37.9	16.7	(59.5)	1,050.7	51.8
Pension (benefit) expense	(32.3)	(20.5)	(14.1)	(7.8)	10.0	6.4	4.0	2.0	(32.3)	10.0	15.3
As Adjusted
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	(1,514.7)	(1,584.1)	(1,750.7)	(1,367.7)	(1,481.9)	(537.4)	(558.1)	(410.1)	(6,217.2)	(2,987.5)	(2,131.6)
Marketing, general and administrative expenses	(775.9)	(779.2)	(777.8)	(699.5)	(752.1)	(277.1)	(311.6)	(249.0)	(3,032.4)	(1,589.8)	(1,038.3)
Special items, net	(3.7)	(4.1)	(16.5)	(3.8)	2,443.4	4.9	(34.5)	108.6	(28.1)	2,522.4	(346.7)
Income tax benefit (expense)	(391.7)	147.4	125.2	65.9	996.3	20.1	21.7	17.1	53.2	(1,055.2)	(61.5)
Net income (loss) from continuing operations									1,412.7	1,995.8	391.3
Net income (loss) attributable to Molson Coors Brewing Company	$ 588.8	$ 287.0	$ 329.9	$ 208.5	$ 1,439.3	$ 207.7	$ 177.9	$ 168.1	$ 1,414.2	$ 1,993.0	$ 395.2
Basic net income (loss) from continuing operations attributable to MCBC per share	$ 2.73	$ 1.33	$ 1.52	$ 0.97	$ 6.70	$ 0.97	$ 0.84	$ 0.83	$ 6.56	$ 9.41	$ 2.11
Basic net income per share (in dollars per share)	2.73	1.33	1.53	0.97	6.70	0.97	0.83	0.83	6.57	9.40	2.13
From continuing operations (in dollars per share)	2.72	1.33	1.52	0.97	6.65	0.96	0.83	0.82	6.52	9.35	2.10
Diluted net income per share (in dollars per share)	$ 2.72	$ 1.33	$ 1.52	$ 0.96	$ 6.65	$ 0.96	$ 0.82	$ 0.82	$ 6.53	$ 9.34	$ 2.12
Consolidated Statements of Comprehensive Income (Loss)
Pension and other postretirement benefit adjustments, net of tax	$ 145.7	$ 0.0	$ 0.0	$ 0.0	$ 53.8	$ 0.0	$ 0.0	$ 0.0	$ 145.7	$ 53.8	$ 19.3
Amortization of net prior service (benefit) cost and net actuarial (gain) loss to income, net of tax	(4.7)	4.6	4.7	(1.0)	10.0	4.2	4.3	4.3	3.6	22.8	16.1
Other comprehensive income (loss), net of tax									714.3	129.4	(833.2)
Consolidated Balance Sheets
Retained earnings	7,206.1	6,705.8	6,507.1	6,265.5	6,145.3	4,794.3	4,674.7	4,585.0	7,206.1	6,145.3
Accumulated other comprehensive income (loss)	(860.0)	(1,070.9)	(1,252.8)	(1,499.1)	(1,571.8)	(1,650.9)	(1,588.8)	(1,449.8)	(860.0)	(1,571.8)
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests	1,436.4	843.1	550.0	215.0	1,998.9	557.4	348.4	168.9	1,436.4	1,998.9	398.5
Income tax (benefit) expense	(53.2)	338.5	191.1	65.9	1,055.2	58.9	38.8	17.1	(53.2)	1,055.2	61.5
Pension (benefit) expense	$ (67.8)	$ (46.9)	$ (31.4)	$ (16.3)	$ (11.6)	$ (11.2)	$ (7.9)	$ (3.8)	(67.8)	(11.6)	(30.1)
Retained earnings
Consolidated Statements of Cash Flows
Net income (loss) including noncontrolling interests									$ 1,414.2	$ 1,993.0	$ 395.2
Accounting Standards Update 2015-10 [Member] | Retained earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets												$ 26.5